build(content_management): add core dependency

- Import core package in archived_headlines_bloc.dart

Author: fulleni

lib/content_management/bloc/archived_headlines/archived_headlines_bloc.dart

@@ -1,4 +1,5 @@
 import 'package:bloc/bloc.dart';
+import 'package:core/core.dart';
 import 'package:equatable/equatable.dart';
 
 part 'archived_headlines_event.dart';